Clinical pure tone audiometry is the most basic hearing test. However, measurements obtained with a standard pure tone audiometer do not take into account the large individual differences in the volume of the ear canal and concomitant differences in the acoustic impedance of the ear. As a result, an audiometer that is calibrated in a standard coupler will provide inaccurate values for the acoustic signal reaching the eardrum. These individual variations in ear canal volume and eardrum impedance can have a substantial effect on the canal pressure due to loading of the canal impedance on the transducer source impedance. The most well known effect is that of standing waves, a frequency dependent change in canal impedance due to reflections resulting primarily from the eardrum load impedance. We propose to develop an instrument based on the Mimosa impedance measurement system that allow for the accurate calibration of the transducer in the canal in a manner that removes the effect of standing waves, and delivers a constant sound intensity to the cochlea. Such an instrument has the potential of greatly reducing errors in clinical audiometry. PUBLIC HEALTH RELEVANCE Pure tone audiometry is the most basic measurement in audiology, yet it is subject to significant errors. The basic problem is the inability of traditional methods of audiometric measurement to correct for the large individual differences in acoustic coupling between the earphone generating the test signals and the human ear. Recent advances in digital signal processing have made it possible to correct for these individual differences in a practical way. This grant will develop a clinical instrument for hearing measurement that will provide accurate measurements of hearing sensitivity that are not subject to the errors of traditional audiometry. [unreadable] [unreadable] [unreadable]